Modern telecommunications systems typically utilize protection techniques to minimize the possibility of faulty data transmission. One form of protection involves transmitting and processing two or more identical or redundant copies of telecommunications signals in the same manner. In other words, there are identical "paths" through which the respective copies of the redundant signals pass and are processed. One path, however, is typically considered active while the duplicate path is considered standby.
The paths, however, typically exist between a pair of network elements such as telecommunications switching systems where data is switched between conducting media. Because of the redundant paths, when a fault is detected in the signals transmitted on the active path, the receiving telecommunications system can switch to obtain the necessary signals from the standby path, thereby avoiding the need to disrupt transmission or service. It is desirable that this switching between paths be done as rapidly and as simply as possible so that it is effectively transparent to the telecommunications system.
In switching devices and methods previously known, when an error was detected in the signal in the active path, that error had to be communicated to an external control system that was outside the data path and that itself controlled switching operations. Thus, when a transmission error or fault was detected in a telecommunications signal by a device or element of the telecommunications switching system, the fault was communicated to the external control system, and a separate device awaited a command from that external control system before performing necessary switching operations. This method is disadvantageous in that communicating an error or fault to an external control system and awaiting switching instructions from that system takes time, and is itself a process that is subject to transmission faults.